DE 697 20 176 T2 discloses a power supply circuit comprising a current source, a power transformer whose secondary side is connected to a circuit arrangement to which power is to be supplied from the power supply circuit, and a voltage-controlled switching element comprising a control connection. In addition, the power supply circuit contains an LC resonant circuit, which is connected in series with the switching element and whose inductance forms the first winding of the power transformer, a feedback winding for supplying a feedback voltage corresponding to a radiofrequency current of the LC resonant circuit to the control connection of the switching element and a bias circuit, which is connected in parallel with the series circuit comprising the LC resonant circuit and the switching element and is connected to the feedback winding in order to supply a bias to the control connection via the feedback winding. Furthermore, the power supply circuit has a bias control circuit for controlling the bias which is connected between the bias circuit and the series circuit comprising the LC resonant circuit and the switching element, and a resistor, which is connected to the control connection of the switching element, wherein the bias and the feedback voltage are supplied to the control connection of the switching element via the resistor, and wherein the resistor is selected to delay the feedback voltage by a preset time period.